[1.6.x] Fixed #21396: Document backwards-incompatible change in RedirectView.get_redirect_url.

Thanks to Tim for the review.

Backport of f2e0266be7 from master.

docs/ref/class-based-views/base.txt

@@ -239,12 +239,23 @@ RedirectView
 
     **Methods**
 
-    .. method:: get_redirect_url(**kwargs)
+    .. method:: get_redirect_url(*args, **kwargs)
 
         Constructs the target URL for redirection.
 
+        .. versionchanged:: 1.6
+
+            The signature of this method was changed to include ``*args``.
+
         The default implementation uses :attr:`url` as a starting
-        string, performs expansion of ``%`` parameters in that string, as well
-        as the appending of query string if requested by :attr:`query_string`.
+        string and performs expansion of ``%`` named parameters in that string
+        using the named groups captured in the URL.
+
+        If :attr:`url` is not set, ``get_redirect_url()`` tries to reverse the
+        :attr:`pattern_name` using what was captured in the URL (both named and
+        unnamed groups are used).
+
+        If requested by :attr:`query_string`, it will also append the query
+        string to the generated URL.
         Subclasses may implement any behavior they wish, as long as the method
         returns a redirect-ready URL string.

docs/releases/1.6.txt

@@ -913,6 +913,12 @@ Miscellaneous
   been removed. Use ``socket.error`` provided by the standard library instead.
   This change was also released in Django 1.5.5.
 
+* The signature of :meth:`django.views.generic.base.RedirectView.get_redirect_url`
+  has changed and now accepts positional arguments as well (``*args, **kwargs``).
+  Any unnamed captured group will now be passed to ``get_redirect_url()``
+  which may result in a ``TypeError`` if you don't update the signature of your
+  custom method.
+
 Features deprecated in 1.6
 ==========================